1. Field of Invention
National Field of Invention
One version of the voltage indicator is intended for single-phase AC voltage detection on 90-130 volt (with respect to ground) rms line cords used in grounded AC power distribution systems as is common in the United States.
2. International Field of Invention
Another version of the voltage indicator is intended for single-phase AC voltage detection on 200-230 volt (with respect to ground) rms line cords used in grounded AC power distribution systems as is common in most countries outside the United States.
2. Description of the Prior Art
Consumers of electric power have long been inconvenienced with the problem of determining whether there is electric power going to an appliance or device that they're about to use. Traditionally they just switch the appliance or device on to see if it works. Not all appliances can be determined to be operable at the moment the power switch is turned on.
Examples of this are coffee makers, soldering irons, and clothes irons that don't have visual power indicators. The failure or unknown question of whether an appliance or device is instantaneously working leads to the natural question; “Is there power going to the appliance or device?” It is the intent of this invention to provide a simple and almost instantaneous answer to this question. Although the present invention doesn't represent a necessity in many applications, it does represent a convenience to expedite the troubleshooting process.
The purpose of this invention is to provide a simple, convenient, and almost instantaneous indication of whether there's an AC single-phase voltage potential present on an AC line cord, but first a discussion of the prior art.
U.S. Pat. No. 5,424,630 to Vazquez (1995) is for a voltage indicator that has a knife blade as one electrical contact and an alligator clip as the other electrical contact of the voltage indicator. The two disadvantages of this indicator are readily apparent. The knife blade contact is used to cut through the insulation on the wire thus permanently damaging it, and the alligator clip needs a grounded electrical terminal to be clipped on to complete the circuit.
U.S. Pat. No. 5,428,288 to Foreman et al. (1995) and U.S. Pat. No. 2,449,150 to Schnoll (1948) are for related indicators. In both of these patents a thin electrical connecting wafer is slid over the male end of a standard electric power plug. A common disadvantage of both of these inventions is that the thin wafer decreases the quality of the electrical connection of the male plug to the power receptacle. The Foreman et al. patent also requires the use of a computer to sense a power failure while in the Schnoll patent the indicator can only be read at the male plug and not at anywhere along the length of the power cord as with the present invention.
U.S. Pat. No. 4,829,289 to Kallman et al. (1989) and Canadian patent 728,300 to Windsor (1966) are for related indicators. The patents are for an illuminated plug that goes between the power receptacle and the male end of the power cord plug. Both of these devices have the disadvantage of being usable at a power receptacle which may be behind a piece of furniture. In the Windsor patent the appliance or device connected to the plug has the additional disadvantage of needing to be turned on in order for the path through the illuminated indicator to be complete.
Swiss patent 221,666 to Gerber (1942) and Canadian patent 474,305 to Simmons (1951) are for related indicators. These two patents are for a screwdriver or pen type of voltage indicator that uses a return path to ground for the indicator circuit through a human being. While the method of using a human as the return path to ground is the same ground return method as in the present invention, the two patents have the disadvantage of needing to make physical contact between the indicator's probe tip and the metal of the conductors under test. The present invention only requires that the indicator be in physical proximity to a power cord under test with no metal-to-metal contact between the conductors of the power cord and the indicator's electrode.
Canadian patent 993,952 to Friesen (1976) is for a power cord voltage indicator in which metallic contacts pierce the conductors of the power cord under test. The piercing of the power cord conductors has the disadvantage of doing permanent damage to the power cord insulation as well as the disadvantage of being unusable on power cords that are completely enclosed in an outer sheath.
U.S. Pat. No. 5,095,265 to Schweitzer Jr. (1992) is for a coaxial power cord voltage indicator in which capacitive sensor must pierce through the outer conductive jacket of the coaxial cable in order to be operative. The patent is limited in use to only coaxial cables in which the outer sheath is electrically conductive due to the need to provide a ground return path. The present invention is usable without piercing the power cord. Other patents to Schweitzer Jr. for related devices are U.S. Pat. No. 5,077,520 (1991), U.S. Pat. No. 5,363,088 (1994) and U.S. Pat. No. 5,070,301 (1991). These are all for coaxial cables with a ground return on the outer coaxial conductor. The present invention uses a human ground return.
U.S. Pat. No. 2,091,521 to Pattison (1937) is for a voltage test instrument that has an analog scale, and it's used one “hot” wire at a time while the present indicator is physically mounted to two or more conductors and only indicates the presence or absence of a voltage without an analog scale.
U.S. Pat. No. 6,157,184 to myself (2000) is for a voltage indicator that uses the same schematic diagram as the present invention while the embodiments of that indicator are very bulky and clumsy compared to the embodiment of the present invention.
A substantial advantage of the present power cord voltage indicator is that it doesn't use a battery or a power source other than the power cord under test. Most voltage indicators use a battery.
Reasons for Utility of Invention
1. Device can be physically mounted anywhere on line cord.
2. Device doesn't physically damage line cord.
3. Circuit breaker or fuse may be tripped or blown at main panel.
4. Incandescent light bulb filament may be burned out.
5. Ground fault circuit interrupter may be tripped.
6. Receptacle may be controlled by a light switch.
7. The plug-in point is at a remote location.
8. The appliance may be burned out or defective.
9. The power cord may have been accidentally yanked from receptacle.
10. Appliance may contain a heating or cooling element that would take several minutes to know if turned on.
11. Catastrophic failure fuse may be blown in appliance.